He talked to area lobstermen, who suspected pollution, then collected water samples from the Acushnet River Estuary and near the Fairhaven Bridge and hurricane barrier.

Back in the lab, he found a possible culprit.

Using sophisticated equipment that separates the molecules of different contaminants in the water, Dr. Zuo identified several types of natural and synthetic estrogen hormones — most likely passed through human waste and released into the river and bay from the nearby Fairhaven and New Bedford wastewater treatment plants.

Dr. Zuo and other scientists suspect that the naturally-occurring and synthetic female estrogen in birth control pills and hormone replacement therapy drugs could be hindering larval lobster development, as well as shell growth and reproduction in adult lobsters.

Estrogen, which mimics lobsters' own molting hormone, may interfere with their molting process and make them more susceptible to the bacteria that causes shell disease.

While estrogen is not the only endocrine disruptor that researchers suspect may contribute to shell disease and other marine life abnormalities, the potency of its synthetic forms make it particularly worrisome.

"We can't say that it's definitely because of estrogen compounds, but it's possible," said Dr. Zuo, who recently received UMass Dartmouth's Scholar of the Year award for his research.

Both male and female hormones are part of a broad, disparate group of chemicals, including ingredients common in pesticides, cosmetics, detergents and other pharmaceuticals, known as endocrine disruptors, so called because they interfere with the endocrine system's ability to regulate growth, development and reproduction in humans, fish and wildlife.

Research has implicated endocrine disruptors in a wide range of health problems, including cancer, reproductive defects, reduced sperm count and immune system disorders.

Knowledge of their environmental and health impacts is relatively new. But amid the thousands of chemicals classified as endocrine disruptors, studies have increasingly focused on hormones like estrogen as suspects in emerging environmental problems.

The presence of estrogen in rivers, lakes and streams has already raised troubling questions about its potential impact on humans and other marine life. For the past decade, studies of fish in rivers near heavily populated urban and suburban areas have shown cause for concern.

One of the most startling recent examples is the Potomac River in Washington, D.C. Federal and state researchers found that at least 80 percent of male bass surveyed in major tributaries that feed the Potomac were growing immature eggs. In the Potomac itself, roughly half of a smaller sample of bass showed signs of so-called feminization.

Research elsewhere in the United States, Canada and Europe has exposed similar phenomena.

To date, no studies have been conducted on whether lobster, fish or other wildlife in SouthCoast's waters show such symptoms of feminization or other abnormalities.

"But this gives us a start," said David Casoni, science liaison for the Massachusetts Lobstermen's Association, whose members want concrete information on what might have contributed to a near 70 percent decline in the local lobster population between 1998 and 2004.

Dr. Zuo is eager to undertake that next stage of research locally, saying concentrations of synthetic estrogens he collected from Buzzards Bay and the Acushnet River — mere milligrams per liter — are still high enough to potentially cause feminization in male fish, he said. He now wants to partner with biologists to examine how development and reproduction of lobsters in Buzzards Bay may be impacted by the potent hormones discharged from nearby municipal wastewater plants.

"This is long-term research," said Dr. Zuo. "It can't produce results right away. It may take a few decades. Once you see the effects, it may be too late."

While scientists slowly zero in on which contaminants in which combinations produce which problems, one thing is certain: wastewater treatment plants are contributing to the contamination.

"What we know from the analytical studies that have been done is that clearly downstream from wastewater treatment plants, when you test waters, they tend to be estrogenic," said Dr. Elaine Francis, national director of the Environmental Protection Agency's endocrine disruptors research program.

That's because most sewage treatment plants in the United States — including those on the SouthCoast — are not designed to remove hormones and myriad other endocrine disrupting chemicals. Each day, these contaminants make their way into streams, rivers and groundwater, and eventually into estuaries and oceans.

"We also know that fish living downstream from wastewater treatment plants are showing signs of impact, and certainly male fish are being feminized in estrogenic waters," said Dr. Francis. She added that the EPA is studying several sewage treatment plants around the country to determine which technologies are most effective at eliminating estrogen from wastewater.

"With the human population increase in the region over the past decade, you reach a threshold that's like turning a switch," said Dr. James Stuart, a University of Connecticut chemistry professor who has studied how lobsters in Long Island Sound and Vineyard Sound are affected by another suspected endocrine disruptor, alkylphenol, common in plastic products.

Dr. Stuart is trying to persuade state environmental protection agencies to increase regulations for the use and disposal of substances containing endocrine disruptors. Like Dr. Zuo, he is concerned that the environmental consequences could be irreversible if policy makers wait for irrefutable proof.

"The effect is there. No one doubts it; it's just about the extent of the problem," he said.

Regulatory agencies are struggling to catch up. Ten years ago, Congress ordered the EPA to undertake a screening program to examine thousands of commercial chemicals and other substances — including human hormones — suspected of interfering with the endocrine system.

After a decade of planning, however, testing is just getting started. Most of the first 50 to 100 chemicals slated for testing this year are pesticides, since that's the group to which people have the most exposure through both water and food, said Dr. Francis of the EPA. Her team is now looking to expand the screening to common male and female hormones.

Even when scientists discover a correlation between an endocrine disrupting chemical and a particular health problem, they face an additional challenge because people are usually exposed to multiple endocrine disruptors at the same time.

That makes research projects like Dr. Zuo's important in beginning to fill in the gaps about the effects of estrogenic hormones.

"We don't know which parameters cause the problems, so we have to isolate each one and then proceed," he said.

"The most important thing is to discover the problem. If we don't discover the problem, we can't find the best way to handle it."

Discovering the problem is the first hurdle. But solving it will not be easy, either. Limited funding makes for piecemeal research. Examining one species' exposure to one chemical in one specific geographic area creates pitfalls for regulation. That's a problem for the people whose livelihoods depend on healthy oceans.

"I look at the ocean as a huge periodic table and we keep putting all these compounds in that trigger other things," said David Casoni. "We have no idea what will affect anything in the ocean. We know the culprits, but where do we go from there?"

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